The check engine light has been on and off since I bought the car, and although the code reader said thermostat and I had it replaced, this problem persists. The engine runs cooler than appropriate, which may be related to that problem, which causes the heater to not be very warm!
At about 100,000 miles, my car overheated while idling for a short period. The radiator was replaced however, the engine still overheats when idling for much more than 15 minutes.
The gears work very hard, and will grind if you don't shift at precisely the right RPM, and always grind while downshifting. I asked the dealer about this problem when I test drove it, and they attributed it to the engine being cold, but this just seems to be a design flaw.
Also around 100,000 miles, a belt began squeaking in the engine at slow speeds, and although I've had it adjusted 2 or 3 times, the problem always recurs. It seems to affect the alternator, I've had it replaced twice in the past year (120,000 and 130,000 miles).
Despite the above problems, this car has been extremely reliable and enduring for the money I paid! I bought it for $3,000 with 63,000 miles on it, and have put 80,000 on it with minimal repairs. Without a doubt this is a basic and somewhat cheaply made car - it doesn't even have a trunk release! If you are looking for luxury or perfection, then this car is not for you.
If you are looking for something reliable, with some annoying, but not devastating problems, then the Rio is a good choice. I am not the best caretaker of my vehicles in terms of oil changes etc, and that, coupled with the miles I've put on, make me very impressed with the way my car has held up. It's very economical, the tires are small and inexpensive, and I get 25-35 mpg. It also handles well as any front wheel car in the snow - I live in the Great Lakes region of NY, and this car has no trouble going through heavy, heavy snow!